G5 Buzz, not the power supply

I recently bought the latest Dual 2.0 G5 and love it, except the buzz that develops randomly (at least I think it's randomly, I can't make it happen yet).

It's not the power supply problem that I've read about, because if I touch the front of the case the buzz goes away. Has anyone else had this problem? Any fixes? I'm sure if I take it to the genius bar I won't be able to make it happen again and it's an hour away.

I have noticed that when I have a CD in the SuperDrive, it sometimes makes the drive door vibrate and buzz a little. Could it be something like tthat? I ask because you said that if you touch the front of the case, it quits.

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